This invention relates to a device for cleaning toner from a moving surface. Although not limited thereto, it is particularly usable in image forming apparatus in which a uniform layer of toner is applied to a surface, the toner is imagewise tacked to the surface, and untacked toner is cleaned off the surface. It can also be used in conventional image forming apparatus.
U.S. patent application Ser. Nos. 07/632,698, now U.S. Pat. No. 5,138,388 (Kamp et al); 07/673,509 (DeBoer et al) now U.S. Pat. No. 5,227,265; 07/621,691, now abandoned (DeBoer et al); and PCT application No. 91/08815, filed Nov. 26, 1991 disclose a process in which a uniform layer of toner is applied to a surface. The toner is imagewise tacked, preferably with a laser, to the surface and then the untacked toner is cleaned off the surface, leaving a toner image corresponding to the tacked toner. The tacked toner image can then be transferred to another surface, or it can be fixed to the surface to which it is tacked. This process can provide extremely high resolution and high density with fine toner particles and a precise laser. It does not require the use of light sensitive materials.
In this process, tacking can be accomplished by softening a heat softenable layer on the image surface, softening a toner particle where it touches the image surface, or both. Toner can be applied by a device comparable to that conventionally used to develop electrostatic images, for example, a magnetic brush development station. However, cleaning is somewhat more difficult, since the loose toner must be cleaned off without disturbing what may be quite lightly tacked imagewise toner. A preferable approach to this cleaning problem is to use a magnetic brush cleaner employing hard magnetic carrier particles and a rotating magnetic core which provides a relatively soft cleaning brush that will clean off the loose toner while leaving the lightly tacked toner image.
U.S. Pat. Nos. 4,734,741; 3,580,673; 4,006,987; 4,110,034 and 4,515,467 are representative of typical magnetic brush cleaners in which a nonmagnetic sleeve is rotated around a stationary core to move cleaning particles attractive to toner past a surface to be cleaned. The cleaning particles are essentially the same as carrier particles used in magnetic brush cleaners. Toner is removed from the cleaning particles by contacting them with a detoning roller which is electrically biased to attract the toner. Toner is scraped off the detoning roller with a blade and falls into a sump for transport by an auger to a toner collection bottle. U.S. Pat. No. 4,279,499 shows a magnetic brush cleaning device having a sump for cleaning particles.
Cleaning of toner off a surface using cleaning particles is dependent upon the amount of toner already on the cleaning particles. Thus, a generic problem with such cleaning devices involves the effectiveness of a continuous detoning operation. This problem is particularly severe in appartus in which large amounts of toner must be cleaned. Thus, the previously described process in which all toner is cleaned off except that tacked, requires much greater detoning than does conventional electrostatic imaging processes.
U.S. Pat. No. 5,148,280; issued Sep. 15, 1992, Hilbert et al, shows a color electrophotographic image forming apparatus in which two color development stations are constructed as a single unit and spring urged toward a photoconductive drum. Toner applying applicators are maintained at a critical spacing whether applying toner or not. A magnetic valving structure is used to turn the stations on and off without changing their position with respect to the drum.